Australian industrial supply mixes metric and imperial measurements across legacy equipment, US-sourced tools, and brand variations. This master conversion reference covers millimetres ↔ inches (decimal and fraction), drill bit number sizes (#1 to #80), letter drill sizes (A to Z), and wire/sheet gauge (AWG and SWG) in a single integrated table — from 0.1mm to over 12mm. Conversion values are calculated arithmetically (mm × 0.03937 = inches, inch × 25.4 = mm) and verified against ANSI B94.11M (twist drills), ASTM B258 (AWG wire diameters), and BS 3737 (SWG).
Master Conversion Table — mm / Inch / Drill # / Drill Letter / AWG / SWG
The headline reference. Each row shows a single physical size with every relevant industrial reference code. Em-dashes (—) indicate the size doesn't have a standard designation in that system. Values are calculated to 3 decimal places (mm) and 4 decimal places (inch).
| mm | inch (decimal) | inch (fraction) | Drill # | Drill Letter | AWG | SWG |
|---|---|---|---|---|---|---|
| 0.079 | 0.0031 | — | — | — | AWG 36 | — |
| 0.100 | 0.0039 | — | — | — | AWG 36 | — |
| 0.127 | 0.0050 | — | — | — | AWG 36 | — |
| 0.200 | 0.0079 | — | — | — | AWG 32 | — |
| 0.203 | 0.0080 | — | — | — | AWG 32 | — |
| 0.254 | 0.0100 | — | — | — | AWG 30 | SWG 32 |
| 0.274 | 0.0108 | — | — | — | AWG 28 | SWG 30 |
| 0.300 | 0.0118 | — | #80 | — | AWG 28 | SWG 30 |
| 0.315 | 0.0124 | — | #80 | — | AWG 28 | SWG 30 |
| 0.321 | 0.0126 | — | #80 | — | AWG 28 | SWG 30 |
| 0.343 | 0.0135 | — | #80 | — | AWG 28 | SWG 28 |
| 0.368 | 0.0145 | 1/64 | #80 | — | AWG 26 | SWG 28 |
| 0.376 | 0.0148 | 1/64 | #80 | — | AWG 26 | SWG 28 |
| 0.397 | 0.0156 | 1/64 | #79 | — | AWG 26 | SWG 28 |
| 0.400 | 0.0157 | 1/64 | #79 | — | AWG 26 | SWG 28 |
| 0.405 | 0.0159 | 1/64 | #79 | — | AWG 26 | SWG 28 |
| 0.406 | 0.0160 | 1/64 | #79 | — | AWG 26 | SWG 28 |
| 0.457 | 0.0180 | — | #77 | — | — | SWG 26 |
| 0.500 | 0.0197 | — | #77 | — | AWG 24 | SWG 26 |
| 0.508 | 0.0200 | — | #76 | — | AWG 24 | — |
| 0.511 | 0.0201 | — | #76 | — | AWG 24 | SWG 24 |
| 0.533 | 0.0210 | — | #76 | — | AWG 24 | SWG 24 |
| 0.559 | 0.0220 | — | #75 | — | AWG 24 | SWG 24 |
| 0.572 | 0.0225 | — | #75 | — | — | SWG 24 |
| 0.600 | 0.0236 | — | #74 | — | AWG 22 | SWG 24 |
| 0.610 | 0.0240 | — | #74 | — | AWG 22 | — |
| 0.635 | 0.0250 | — | #73 | — | AWG 22 | — |
| 0.644 | 0.0254 | — | #73 | — | AWG 22 | — |
| 0.660 | 0.0260 | — | #72 | — | AWG 22 | — |
| 0.700 | 0.0276 | — | #71 | — | — | SWG 22 |
| 0.711 | 0.0280 | — | #70 | — | — | SWG 22 |
| 0.742 | 0.0292 | — | #70 | — | — | SWG 22 |
| 0.787 | 0.0310 | 1/32 | #69 | — | AWG 20 | — |
| 0.794 | 0.0313 | 1/32 | #68 | — | AWG 20 | — |
| 0.800 | 0.0315 | 1/32 | #68 | — | AWG 20 | — |
| 0.812 | 0.0320 | 1/32 | #68 | — | AWG 20 | — |
| 0.813 | 0.0320 | 1/32 | #68 | — | AWG 20 | — |
| 0.838 | 0.0330 | 1/32 | #67 | — | AWG 20 | — |
| 0.889 | 0.0350 | — | #65 | — | — | SWG 20 |
| 0.900 | 0.0354 | — | #65 | — | — | SWG 20 |
| 0.914 | 0.0360 | — | #65 | — | — | SWG 20 |
| 0.940 | 0.0370 | — | #64 | — | — | SWG 20 |
| 0.965 | 0.0380 | — | #63 | — | — | — |
| 0.991 | 0.0390 | — | #62 | — | AWG 18 | — |
| 1.000 | 0.0394 | — | #62 | — | AWG 18 | — |
| 1.016 | 0.0400 | — | #61 | — | AWG 18 | — |
| 1.024 | 0.0403 | — | #61 | — | AWG 18 | — |
| 1.041 | 0.0410 | — | #61 | — | AWG 18 | — |
| 1.067 | 0.0420 | — | #59 | — | AWG 18 | — |
| 1.092 | 0.0430 | — | #58 | — | — | — |
| 1.181 | 0.0465 | 3/64 | #56 | — | — | SWG 18 |
| 1.191 | 0.0469 | 3/64 | #56 | — | — | SWG 18 |
| 1.219 | 0.0480 | 3/64 | #56 | — | — | SWG 18 |
| 1.290 | 0.0508 | — | #55 | — | AWG 16 | — |
| 1.321 | 0.0520 | — | #55 | — | AWG 16 | — |
| 1.397 | 0.0550 | — | #54 | — | — | — |
| 1.500 | 0.0591 | — | #53 | — | — | — |
| 1.511 | 0.0595 | — | #53 | — | — | — |
| 1.587 | 0.0625 | 1/16 | #52 | — | AWG 14 | SWG 16 |
| 1.613 | 0.0635 | 1/16 | #52 | — | AWG 14 | SWG 16 |
| 1.626 | 0.0640 | 1/16 | #52 | — | AWG 14 | SWG 16 |
| 1.628 | 0.0641 | 1/16 | #52 | — | AWG 14 | SWG 16 |
| 1.702 | 0.0670 | — | #51 | — | — | — |
| 1.778 | 0.0700 | — | #50 | — | — | — |
| 1.854 | 0.0730 | — | #49 | — | — | — |
| 1.930 | 0.0760 | — | #48 | — | — | — |
| 1.984 | 0.0781 | 5/64 | #47 | — | — | SWG 14 |
| 1.994 | 0.0785 | 5/64 | #47 | — | — | SWG 14 |
| 2.000 | 0.0787 | 5/64 | #47 | — | — | SWG 14 |
| 2.032 | 0.0800 | 5/64 | #47 | — | AWG 12 | SWG 14 |
| 2.053 | 0.0808 | — | #46 | — | AWG 12 | SWG 14 |
| 2.057 | 0.0810 | — | #46 | — | AWG 12 | SWG 14 |
| 2.083 | 0.0820 | — | #46 | — | AWG 12 | — |
| 2.184 | 0.0860 | — | #44 | — | — | — |
| 2.261 | 0.0890 | — | #43 | — | — | — |
| 2.375 | 0.0935 | 3/32 | #42 | — | — | — |
| 2.381 | 0.0937 | 3/32 | #42 | — | — | — |
| 2.438 | 0.0960 | — | #41 | — | — | — |
| 2.489 | 0.0980 | — | #40 | — | — | — |
| 2.500 | 0.0984 | — | #40 | — | — | — |
| 2.527 | 0.0995 | — | #40 | — | — | — |
| 2.578 | 0.1015 | — | #38 | — | AWG 10 | — |
| 2.588 | 0.1019 | — | #38 | — | AWG 10 | — |
| 2.642 | 0.1040 | — | #37 | — | — | SWG 12 |
| 2.705 | 0.1065 | — | #36 | — | — | — |
| 2.778 | 0.1094 | 7/64 | #35 | — | — | — |
| 2.794 | 0.1100 | 7/64 | #35 | — | — | — |
| 2.819 | 0.1110 | 7/64 | #35 | — | — | — |
| 2.870 | 0.1130 | — | #33 | — | — | — |
| 2.946 | 0.1160 | — | #32 | — | — | — |
| 3.000 | 0.1181 | — | #31 | — | — | — |
| 3.048 | 0.1200 | — | #31 | — | — | — |
| 3.175 | 0.1250 | 1/8 | — | — | — | — |
| 3.251 | 0.1280 | — | #30 | — | AWG 8 | SWG 10 |
| 3.264 | 0.1285 | — | #30 | — | AWG 8 | SWG 10 |
| 3.454 | 0.1360 | — | #29 | — | — | — |
| 3.500 | 0.1378 | — | #29 | — | — | — |
| 3.569 | 0.1405 | 9/64 | #28 | — | — | — |
| 3.572 | 0.1406 | 9/64 | #28 | — | — | — |
| 3.658 | 0.1440 | — | #27 | — | — | — |
| 3.734 | 0.1470 | — | #26 | — | — | — |
| 3.797 | 0.1495 | — | #25 | — | — | — |
| 3.861 | 0.1520 | — | #24 | — | — | — |
| 3.912 | 0.1540 | — | #23 | — | — | — |
| 3.969 | 0.1563 | 5/32 | #22 | — | — | — |
| 3.988 | 0.1570 | 5/32 | #22 | — | — | — |
| 4.000 | 0.1575 | 5/32 | #22 | — | — | — |
| 4.039 | 0.1590 | — | #21 | — | — | SWG 8 |
| 4.064 | 0.1600 | — | #21 | — | — | SWG 8 |
| 4.089 | 0.1610 | — | #20 | — | AWG 6 | SWG 8 |
| 4.115 | 0.1620 | — | #20 | — | AWG 6 | — |
| 4.216 | 0.1660 | — | #19 | — | — | — |
| 4.305 | 0.1695 | — | #18 | — | — | — |
| 4.366 | 0.1719 | 11/64 | #17 | — | — | — |
| 4.394 | 0.1730 | 11/64 | #17 | — | — | — |
| 4.496 | 0.1770 | — | #16 | — | — | — |
| 4.500 | 0.1772 | — | #16 | — | — | — |
| 4.572 | 0.1800 | — | #15 | — | — | — |
| 4.623 | 0.1820 | — | #14 | — | — | — |
| 4.700 | 0.1850 | — | #13 | — | — | — |
| 4.762 | 0.1875 | 3/16 | #12 | — | — | — |
| 4.800 | 0.1890 | 3/16 | #12 | — | — | — |
| 4.851 | 0.1910 | — | #11 | — | — | SWG 6 |
| 4.877 | 0.1920 | — | #11 | — | — | SWG 6 |
| 4.915 | 0.1935 | — | #10 | — | — | SWG 6 |
| 4.978 | 0.1960 | — | #9 | — | — | — |
| 5.000 | 0.1969 | — | #9 | — | — | — |
| 5.055 | 0.1990 | — | #8 | — | — | — |
| 5.105 | 0.2010 | — | #7 | — | — | — |
| 5.159 | 0.2031 | 13/64 | #6 | — | AWG 4 | — |
| 5.182 | 0.2040 | 13/64 | #6 | — | AWG 4 | — |
| 5.189 | 0.2043 | 13/64 | #6 | — | AWG 4 | — |
| 5.220 | 0.2055 | — | #6 | — | AWG 4 | — |
| 5.309 | 0.2090 | — | #4 | — | — | — |
| 5.410 | 0.2130 | — | #3 | — | — | — |
| 5.556 | 0.2187 | 7/32 | — | — | — | — |
| 5.613 | 0.2210 | — | #2 | — | — | — |
| 5.791 | 0.2280 | — | #1 | — | — | — |
| 5.893 | 0.2320 | — | — | — | — | SWG 4 |
| 5.944 | 0.2340 | 15/64 | — | A | — | — |
| 5.953 | 0.2344 | 15/64 | — | A | — | — |
| 6.000 | 0.2362 | 15/64 | — | B | — | — |
| 6.045 | 0.2380 | — | — | B | — | — |
| 6.147 | 0.2420 | — | — | C | — | — |
| 6.248 | 0.2460 | — | — | D | — | — |
| 6.350 | 0.2500 | 1/4 | — | E | — | — |
| 6.528 | 0.2570 | — | — | F | AWG 2 | — |
| 6.544 | 0.2576 | — | — | F | AWG 2 | — |
| 6.629 | 0.2610 | — | — | G | — | — |
| 6.747 | 0.2656 | 17/64 | — | H | — | — |
| 6.756 | 0.2660 | 17/64 | — | H | — | — |
| 6.909 | 0.2720 | — | — | I | — | — |
| 7.000 | 0.2756 | — | — | J | — | SWG 2 |
| 7.010 | 0.2760 | — | — | J | — | SWG 2 |
| 7.036 | 0.2770 | — | — | J | — | SWG 2 |
| 7.137 | 0.2810 | 9/32 | — | K | — | — |
| 7.144 | 0.2813 | 9/32 | — | K | — | — |
| 7.348 | 0.2893 | — | — | L | AWG 1 | — |
| 7.366 | 0.2900 | — | — | L | AWG 1 | — |
| 7.493 | 0.2950 | 19/64 | — | M | — | — |
| 7.541 | 0.2969 | 19/64 | — | M | — | — |
| 7.620 | 0.3000 | — | — | — | — | SWG 1 |
| 7.671 | 0.3020 | — | — | N | — | — |
| 7.938 | 0.3125 | 5/16 | — | — | — | — |
| 8.000 | 0.3150 | — | — | O | — | — |
| 8.026 | 0.3160 | — | — | O | — | — |
| 8.204 | 0.3230 | — | — | P | AWG 0 (1/0) | SWG 0 |
| 8.230 | 0.3240 | — | — | P | AWG 0 (1/0) | SWG 0 |
| 8.252 | 0.3249 | — | — | P | AWG 0 (1/0) | SWG 0 |
| 8.334 | 0.3281 | 21/64 | — | — | — | — |
| 8.433 | 0.3320 | — | — | Q | — | — |
| 8.611 | 0.3390 | — | — | R | — | — |
| 8.731 | 0.3437 | 11/32 | — | — | — | — |
| 8.839 | 0.3480 | — | — | S | — | SWG 2/0 |
| 9.000 | 0.3543 | — | — | — | — | — |
| 9.093 | 0.3580 | 23/64 | — | T | — | — |
| 9.128 | 0.3594 | 23/64 | — | T | — | — |
| 9.266 | 0.3648 | — | — | — | AWG 00 (2/0) | — |
| 9.347 | 0.3680 | — | — | U | — | — |
| 9.449 | 0.3720 | — | — | — | — | SWG 3/0 |
| 9.525 | 0.3750 | 3/8 | — | — | — | — |
| 9.576 | 0.3770 | — | — | V | — | — |
| 9.804 | 0.3860 | — | — | W | — | — |
| 9.922 | 0.3906 | 25/64 | — | — | — | — |
| 10.000 | 0.3937 | — | — | — | — | — |
| 10.084 | 0.3970 | — | — | X | — | — |
| 10.160 | 0.4000 | — | — | — | — | SWG 4/0 |
| 10.262 | 0.4040 | — | — | Y | — | — |
| 10.319 | 0.4063 | 13/32 | — | — | — | — |
| 10.404 | 0.4096 | — | — | — | AWG 000 (3/0) | — |
| 10.490 | 0.4130 | — | — | Z | — | — |
| 10.716 | 0.4219 | 27/64 | — | — | — | — |
| 10.973 | 0.4320 | — | — | — | — | SWG 5/0 |
| 11.000 | 0.4331 | — | — | — | — | SWG 5/0 |
| 11.112 | 0.4375 | 7/16 | — | — | — | — |
| 11.509 | 0.4531 | 29/64 | — | — | — | — |
| 11.684 | 0.4600 | — | — | — | AWG 0000 (4/0) | — |
| 11.786 | 0.4640 | — | — | — | — | SWG 6/0 |
| 11.906 | 0.4687 | 15/32 | — | — | — | — |
| 12.000 | 0.4724 | — | — | — | — | — |
| 12.303 | 0.4844 | 31/64 | — | — | — | — |
| 12.700 | 0.5000 | 1/2 | — | — | — | SWG 7/0 |
| 13.000 | 0.5118 | — | — | — | — | — |
| 13.494 | 0.5313 | 17/32 | — | — | — | — |
| 14.000 | 0.5512 | — | — | — | — | — |
| 14.287 | 0.5625 | 9/16 | — | — | — | — |
| 15.000 | 0.5906 | — | — | — | — | — |
| 15.081 | 0.5937 | 19/32 | — | — | — | — |
| 15.875 | 0.6250 | 5/8 | — | — | — | — |
| 16.000 | 0.6299 | — | — | — | — | — |
| 16.669 | 0.6563 | 21/32 | — | — | — | — |
| 17.462 | 0.6875 | 11/16 | — | — | — | — |
| 18.000 | 0.7087 | — | — | — | — | — |
| 18.256 | 0.7187 | 23/32 | — | — | — | — |
| 19.050 | 0.7500 | 3/4 | — | — | — | — |
| 19.844 | 0.7813 | 25/32 | — | — | — | — |
| 20.000 | 0.7874 | — | — | — | — | — |
| 20.637 | 0.8125 | 13/16 | — | — | — | — |
| 21.431 | 0.8437 | 27/32 | — | — | — | — |
| 22.225 | 0.8750 | 7/8 | — | — | — | — |
| 23.019 | 0.9063 | 29/32 | — | — | — | — |
| 23.812 | 0.9375 | 15/16 | — | — | — | — |
| 24.606 | 0.9687 | 31/32 | — | — | — | — |
| 25.000 | 0.9843 | — | — | — | — | — |
| 25.400 | 1.0000 | 1 | — | — | — | — |
Sources: ANSI B94.11M (Twist Drills — number and letter sizes), ASTM B258 (Standard Specification for Standard Nominal Diameters and Cross-Sectional Areas of AWG Sizes), BS 3737 (Imperial Standard Wire Gauge), Machinery's Handbook 31st Edition. Conversion arithmetic: 1 inch = 25.4mm exact.
Drill Bit Number Sizes (#1 to #80) — Origin and Use
Number drill sizes are an American imperial heritage system that fills the gap between fractional drill sizes at small diameters. The system runs from #1 (5.791mm / 0.2280") DOWN to #80 (0.343mm / 0.0135").
Critical counter-intuitive convention: HIGHER number = SMALLER drill. A #80 is the smallest commercial twist drill commonly available; #1 is the largest in the number series before letter sizes begin.
Number drills are found on: US-sourced precision drills, gunsmithing tooling, model engineering, jeweller's drills, and increasingly on imported European-marked tools that follow the ANSI B94.11M dimensional standard. The mm equivalents are fixed per the standard — they don't follow a clean formula because the system predates the metric era.
Letter Drill Sizes (A to Z) — Filling the Gap Between Numbers and Fractions
Letter drills fill the dimensional gap between the largest number drill (#1 at 5.79mm) and ¼" (6.35mm), then continue up to just under ⅜" (9.53mm). Range: A (5.944mm / 0.234") to Z (10.490mm / 0.413").
Critical counter-intuitive convention: HIGHER letter = LARGER drill (opposite to the number system). A = smallest letter drill (just above #1); Z = largest letter drill (just below ⅜").
Used on US-sourced precision drills, machine shops following ANSI B94.11M, and in tap-drill selection charts where the standard recommends a letter-size drill before a particular tap.
Wire & Sheet Metal Gauges (AWG vs SWG)
AWG — American Wire Gauge
Dominant US wire and light-sheet system. Per ASTM B258, AWG diameter is calculated as: diameter in inches = 0.005 × 92^((36 − N) / 39). Each step in gauge number corresponds to a 1.122× change in diameter. AWG #0000 (4/0) is 11.684mm; AWG #40 is 0.079mm.
Counter-intuitive convention: HIGHER gauge number = THINNER material. AWG 12 (2.053mm) is thicker than AWG 18 (1.024mm).
SWG — British Imperial Standard Wire Gauge
Heritage British wire and sheet system, per BS 3737. SWG uses different numerical values to AWG — SWG 18 = 1.219mm but AWG 18 = 1.024mm. Same gauge number, different physical size.
Practical impact: when ordering wire or sheet from international suppliers, always confirm whether the gauge is AWG or SWG. The 0.2mm difference matters in electrical and structural applications.
BWG — Birmingham Wire Gauge (Tube and Sheet)
Most commonly seen on tube wall thickness specifications (e.g. "16 BWG tube wall = 1.651mm"). BWG values for sheet steel approximate but don't equal AWG or SWG. For comprehensive AWG ↔ SWG ↔ BWG conversion specifically for sheet metal applications, see our dedicated Sheet Metal & Wire Gauge Chart.
Common Conversion Pitfalls
- "M8" is NOT 8mm hole. M8 = a metric thread with nominal diameter 8mm and standard pitch 1.25mm. The tap drill (hole before tapping) is M8 − pitch = 6.75mm. Use the metric thread designation for fastener selection, the calculated tap drill for hole drilling.
- "5/16" is NOT exactly 8mm. 5/16" = 7.938mm, a 0.062mm difference from 8mm. Close enough for many applications, NOT close enough for press fits, bearings, or precision tolerances.
- Drill #2 ≠ 2mm. Number drills don't correlate with mm. Drill #2 = 5.613mm. Always use the conversion chart.
- AWG 12 ≠ 12mm. AWG 12 = 2.053mm wire diameter. Wire gauge numbers don't correlate with mm at all.
- Gauge numbers are backwards. Higher gauge = thinner material. Counter-intuitive but consistent across AWG, SWG, BWG.
- Letter drills are backwards from number drills. Higher letter = larger drill (A small, Z large). Higher number = smaller drill (#1 large, #80 small). The two systems use opposite conventions.
Quick Conversion Formulas (Memorise These)
- mm to inch: divide by 25.4 (or rough "÷ 25" for mental approximation)
- inch to mm: multiply by 25.4 (or rough "× 25" for mental approximation)
- Metric thread tap drill: Ø − pitch (e.g. M8 × 1.25 → tap drill 6.75mm)
- AWG to mm (formula): diameter = 0.127 × 92^((36 − N) / 39)
- Inch decimal to fraction (rough): multiply decimal by 64, round to nearest whole number, simplify fraction (e.g. 0.1875 × 64 = 12, → 12/64 = 3/16)
Frequently Asked Questions
Q: What's 3/16" in mm?
3/16" = 0.1875" = 4.7625mm, typically rounded to 4.76mm or stated as 4.8mm. Equivalent to #14 drill (0.180" / 4.572mm) at the lower end of tolerance, or just above letter drill 'A' (0.234" / 5.944mm) at the upper end.
Q: What's 10mm in inches?
10mm = 0.3937". Closest imperial fraction is 25/64" = 0.3906" (0.10mm undersize). No exact fractional equivalent — for tight tolerances, use 10mm direct rather than substitute 25/64" or 13/32".
Q: What size drill is M8?
M8 with standard coarse pitch (M8 × 1.25): tap drill is M8 − 1.25 = 6.75mm. M8 with fine pitch (M8 × 1.0): tap drill 7.0mm. The thread diameter (M8 = 8.0mm) is NOT the same as the drill size.
Q: AWG 12 = how many mm?
AWG 12 = 0.0808" = 2.053mm. Used for general-purpose electrical wiring carrying ~20-25 amperes. Note that AWG sizes are wire DIAMETERS, not areas or cross-sections.
Q: What is a #7 drill bit in mm?
#7 drill bit = 0.2010" = 5.105mm. Sits between 5mm and 5.5mm metric. Commonly used as a pilot drill or in thread-drilling charts for specific UNC/UNF tap-drill recommendations.
Q: What's the difference between AWG and SWG?
AWG (American Wire Gauge, ASTM B258) and SWG (Imperial Standard Wire Gauge, BS 3737) use the same gauge numbering but different actual diameters. AWG 18 = 1.024mm. SWG 18 = 1.219mm. AWG is dominant in US/Canadian electrical work and increasingly in light-sheet applications. SWG persists in UK and Commonwealth countries for heritage applications. Always confirm which standard when ordering.
Q: Is 1/4" the same as 6mm?
Close but not equal. 1/4" = 6.350mm — 0.350mm larger than 6mm. For most engineering applications the difference matters: bolt clearance holes (use 6.5mm for 1/4" bolts), bearing fits (don't substitute), tube fittings (always confirm the actual ID requirement). For DIY/general purpose, often close enough.
Q: What's the metric equivalent of a 5/16" socket?
5/16" = 7.938mm. Closest metric socket is 8mm — 0.062mm oversize, which is normally acceptable but slightly looser fit than the exact match. For automotive work on US-sourced vehicles, use the exact 5/16" socket where available.
Q: How big is a 1mm drill in inches?
1mm = 0.0394". Closest fractional equivalent: 1/32" = 0.03125" (0.20mm smaller), then 3/64" = 0.0469" (0.20mm larger). Closest number drill: #60 = 0.0400" / 1.016mm — practically identical to 1mm for most applications.
Q: What gauge is 0.5mm sheet metal?
0.5mm sheet thickness corresponds approximately to AWG 24 (0.511mm) or SWG 25 (0.508mm). Industry typically specifies sheet metal in mm directly in Australia; gauge numbers persist for imported US/UK material.
Q: Why are higher gauge numbers thinner?
Historical artefact of how wire-drawing was scaled. In the original wire-drawing process, each drawing step reduced the wire diameter through a smaller die — the gauge number counted the number of draws. So a 'higher gauge' wire had been drawn through more dies, ending up thinner. The convention is preserved across all wire gauge systems (AWG, SWG, BWG) and applies equally to sheet metal gauges.
Q: How do I convert decimal inches to fractions?
Multiply the decimal by 64 (the smallest common denominator), round to the nearest whole number, then simplify the fraction. Example: 0.1875 × 64 = 12 → 12/64 → simplifies to 3/16. Example: 0.250 × 64 = 16 → 16/64 → simplifies to 1/4. For tighter precision, multiply by 128 (use 128ths) instead of 64.
Q: What's M10 in imperial?
M10 metric thread (10mm nominal diameter, 1.5mm coarse pitch) has no exact imperial equivalent. Closest: 3/8" UNC (16 TPI) = 9.525mm nominal — 0.475mm smaller than M10. The thread profiles differ (M10 has a 60° flank; 3/8 UNC also 60°), and pitches are different (M10 × 1.5mm vs 3/8 × 1.5875mm for 16 TPI). Don't interchange — use the original specification.
Q: What's 25mm in inches?
25mm = 0.9843" — just under 1 inch. Closest fractional equivalent is 1" (25.4mm), which is 0.4mm oversize. For tight applications, use 25mm directly. For general purposes, 1" is often acceptable.
Q: Is 3.18mm exactly 1/8"?
Essentially yes — 1/8" = 0.125" = 3.175mm exactly. 3.18mm is a rounded approximation that introduces a 0.005mm error. For most workshop applications, treat 3.18mm and 1/8" as interchangeable. For precision (bearing fits, gauge blocks), use 3.175mm or the exact fractional inch.
Related AIMS Engineering Reference Guides
- Workpiece Material Cross-Reference Chart — sister master reference (materials)
- Cutting Speeds & Feeds Master Reference
- Cutting Tool Troubleshooting Master
- Cutting Tool Coatings Guide
- Cutting Tool Materials Guide
- Drill Bit Metric / Imperial Size Chart (child article)
- Fastener Reference Guide — Metric / Imperial (child article)
- Socket Size Chart — Metric / Imperial (child article)
- Spanner Size Chart — Metric / Imperial (child article)